1. Field of the Invention
The present invention generally relates to selectively etching nitride in a chemical downstream etching process, and more particularly to an etching process that uses CH2F2 to etch and convert the nitride regions into surface mediated uniform reactive film (SMURF) regions comprising (NH4)2SiF6.
2. Description of the Related Art
The standard process for highly selective isotropic nitride etching is a wet process, e.g., a hot phosphoric acid bath. This process suffers from the following drawbacks. It is difficult to control the etch rate and etch selectively over the life of the bath. This wet etching also has poor cross wafer uniformity (>20% 3σ). Also, the requirement for timed overetching approaches 50% with this process. Further, this etching chemistry is not compatible with resist or polysilicon and there are severe environmental handling and disposal issues with phosphoric acid. The phosphoric acid additionally has contamination issues with Cu, which can have undesired effects on devices.
Alternate dry etch process have been offered which have a severe tradeoff between an acceptable nitride etch rate (>2000 A/min) and nitride/oxide etch selectivity (>50:1). Additionally, the reaction mechanisms are not understood conventionally and general prescriptions of process control have not been offered. The invention described below addresses these concerns.